It is known to use laser-based and/or imager-based readers in a dual window or bi-optical workstation to electro-optically read indicia, such as bar code symbols, associated with three-dimensional products to be identified and processed, e.g., purchased, at a point-of-transaction workstation provided at a countertop of a checkout stand in supermarkets, warehouse clubs, department stores, and other kinds of retailers. The products are typically slid or moved across, or presented to a central region of, a generally horizontal window that faces upwardly above the countertop and/or a generally vertical or upright window that vertically faces a user at the workstation. When at least one laser scan line generated by a laser-based reader sweeps over a symbol and/or when return light from the symbol is captured over a field of view by a solid-state imager of an imager-based reader, the symbol is then processed, decoded and read, thereby identifying the product.
The symbol may be located low or high, or right to left, on the product, or anywhere in between, on any of six sides of the product. The symbol may be oriented in a “picket fence” orientation in which elongated parallel bars of a one-dimensional Universal Product Code (UPC) symbol are vertical, or in a “ladder” orientation in which the UPC symbol bars are horizontal, or at any orientation angle in between. The products may be held by the user at various tilt angles during their movement across, or presentation to, either window. The products may be positioned either in contact with, or held at a distance away from, either window during such movement or presentation. All these factors make the symbol location variable and difficult to predict in advance.
In such an environment, it is important that the readers at the workstation provide a full coverage scan zone above the horizontal window and in front of the vertical window so that the scan zone extends down as close as possible to the countertop, and sufficiently high above the countertop, and as wide as possible across the width of the countertop. The scan zone projects into space away from the windows and grows in volume rapidly in order to cover symbols on products that are positioned not only on the windows, but also many inches therefrom. The scan zone must be large enough to read symbols positioned in any possible way across the entire volume of the scan zone and must not have any dead areas in which symbols are not covered and, therefore, cannot be read.
As advantageous as workstations with laser-based readers have been in processing transactions, workstations with imager-based readers, also known as imagers, are thought to offer improved reliability and have the added capability of reading indicia other than UPC symbols, such as two-dimensional or stacked or truncated symbols, as well as the capability of imaging non-symbol targets, such as receipts, driver's licenses, signatures, etc. It was initially thought that an all imager-based workstation would require about ten to twelve imagers in order to provide a full coverage scan zone to enable reliable reading of indicia that could be positioned anywhere on all six sides of a three-dimensional product. However, to bring the cost of the imager-based workstation down to an acceptable level, it is known to reduce the need for so many imagers by splitting the field of view of at least one imager into light collection regions.
However, such light collection regions produced by splitting the field of view in the known imager-based workstation do not fully occupy the scan zone. As a result, the scan zone does not have full coverage and has dead areas in which indicia cannot be read. Also, such light collection regions are generally symmetrical, i.e., have the same size and spatial volume. As a result, if one of the light collection regions is sized to read only one side of a product, then another of the light collection regions, that is tasked to read two sides of the product, would not be large enough to reliably perform its task if both light collection regions had the same size. It would be desirable if different light collection regions had different sizes to perform different tasks. In addition, such light collection regions are twisted or skewed relative to the windows through which they pass. As a result, a peripheral portion of the twisted light collection region is clipped and blocked by a workstation wall bounding the window. All these factors, of course, degrade reading performance and efficiency.